The present invention relates to tapered, corrugated spacer members of the type commonly used to maintain a desired spacing between successive folds or pleats of accordion pleated, high-efficiency air filter media. More specifically, the invention relates to a novel form of such spacer members, folded in zig-zag fashion along parallel lines with a greater number of V formations within a given width along one edge of the sheet than previously achieved in practise.
In a common commercial form of high efficiency air filter, a length of filter media is folded in accordion fashion to provide a succession of V-shaped pleats, and sealed about its periphery to an open, rectangular frame. The surfaces of adjacent pleats are often spaced by less than 2/10ths of an inch at the open end, i.e., at the widest spacing, and gradually merge to the closed end. Consequently, it is necessary to place spacer means between each of the adjacent media walls to maintain the air flow through the filter at the highest volume and lowest pressure drop commensurate with the desired efficiency level.
Corrugated sheets of aluminum, or other materials, which are tapered in some manner from one edge of the opposite edge have long been utilized to provide the necessary spacing of the media pleats in such filters. For example, U.S. Pat. No. 2,720,937 of Root, Jr. discloses spacer members of the type referred to, as do Patent Nos. 3,146,197 of Getzin and 3,293,833 of Barany. The present invention is most closely related to the latter of these and represents an improvement in that a more gradual taper is provided, down to a smaller amplitude, as will later become apparent.
The ratio of the amplitudes, i.e., the linear distance between parallel lines extending laterally of the spacers through the successive fold lines on each side, along the two opposite edges having the V formations, is the same as the ratio of the number of V formations within a given width at the opposite edges. That is, in order to maintain parallel fold lines, if three V formations are made at one edge for every one V formation at the other, the height at the small amplitude edge will be one-third of that at the high amplitude edge. Likewise, if five V formations are made at the small amplitude end for every one at the large amplitude end, the ratio of both amplitudes and number of V formations within a given linear distance will be five to one.
Although the advantages of a 5 to 1 ratio over a 3 to 1 ratio in tapered separators of this type has long been recognized, and Barany Pat. No. 3,293,833 states that the ratio may be any odd whole number, it has never been possible in practise to fabricate satisfactory spacers with forming rolls and blades such as shown in the patent having a higher than 3 to 1 ratio. That is, U.S. Pat. No. 3,293,833, and its companion U.S. Pat. No. 3,311,526 covering the preferred form of apparatus for fabricating the spacers, both of which are assigned to applicant's assignee, imply that the ratio may be changed merely by increasing the number of small amplitude forming blades on each side of the large amplitude blades. However, when this was attempted in forming spacers having large amplitude folds in the dimensional range required, many breaks and cracks occurred along the small amplitude edge. Spacers having such breaks or cracks are unsuitable for use since the burrs and sharp edges may tear or perforate the filter media, rendering the entire filter pack unacceptable.
Furthermore, in order to provide spacers having the necessary rigidity and resistance to flattening after the V formations have been made, it is desirable to use aluminum sheet of some minimum hardness, consistent with the requirement that the formed spacers be essentially free of breaks and cracks. In the past, it was considered unfeasible to produce a spacer with a 5 to 1 taper ratio, even with soft aluminum, having some capability of stretching without breaking.
It is also a desireable feature that the spacers not only have a higher ratio of amplitude from high to low end, but also that the taper be as even as possible from end to end. Although the V formations extending completely from end to end of the spacers, i.e., those fold lines included at the high amplitude end, may exhibit such gradual taper, the fold lines forming the intermediate V formations at the low amplitude end cannot extend entirely to the high amplitude end if the high amplitude V formations are to be maintained. Consequently, in order to achieve the most even and gradual taper, the fold lines forming the intermediate fold lines at the low amplitude end should extend to a point about 80% to 90% of the distance from the low to the high amplitude edge. Although the spacers are shown in aforementioned U.S. Pat. No. 3,293,833, particularly in FIG. 4, as having intermediate fold lines extending about 90% of such distance, in actual practise spacers commercially produced over the past 20-odd years have not been able to achieve configurations wherein the intermediate fold lines extended more than about 35% to 50% of the distance from low to high amplitude ends.
Thus, while the advantages and desireability of corrugated aluminum spacers tapering from a desired amplitude at one end to approximately 1/5 that amplitude at the other have long been recognized, satisfactory spacers of this type have never been produced on a commercial scale by the preferred means of passing aluminum sheet between a pair of rotating rolls having forming blades to engage and fold the sheet material. Also, spaces having the desired high degree of hardness, and intermediate fold lines extending from the low amplitude end to a point about 90% of the distance to the high amplitude end have not been achieved in commercial practise.
It is a principal object of the present invention to provide high efficiency air filters of the accordion-pleated media type wherein consecutive pleats are held in spaced relation at the open end on both upstream and downstream sides and taper more evenly from the open end to a sharper fold at the closed end than similar prior art units.
It is a further principle object to provide an article of manufacture in the form of a corrugated aluminum sheet folded in zig-zag fashion along substantially parallel fold lines to provide a succession of V formations of uniform width and amplitude along one edge and V formations of substantially 1/5 said uniform width and spacing along the opposite edge, where the amplitude is on the order of 0.03 to 0.04 inches.
It is a further object to provide a corrugated aluminum spacer for accordion-pleated air filters which is folded by forming blades on rotating rolls between which the aluminum sheet is passed, such folds having a much lower amplitude than prior art spacers without a significant number of cracks, tears or breaks in the formed spacer.
Another object is to provide a zig-zag folded spacer of the type referred to, having a 5 to 1 ratio of amplitude from high to low end, with a substantially even taper in that the fold lines forming the intermediate V formations at the low amplitude end extend approximately 90% of the distance to the high amplitude end.
Other objects will in part be obvious and will in part appear hereinafter.